This directive forbids access unless HTTP over SSL (that is HTTPS) is enabled for the current
connection. It is very handy inside the SSL-enabled virtual host or directories as a defense
against configuration errors that expose data that should be protected. When this directive
is present, all requests that do not use SSL are denied.

The FAQ entry you referenced discusses setting up your website to support SSL, the directive
SSLRequireSSL is what you would use to specify restrictions per the whole site (or the specific
Alias/Directories within your site.)

You can redirect http://example.com/ to https://example.com/, but it means that clear-text HTTP is still being used just to send the HTTP Redirect.

This exposes the user to attacks by tools such as sslstrip, unless he carefully checks every time that the domain is really https://example.com, not http://example.com/, not https://examp1e.com, not https://(insert non-Latin homoglyphs here).com...

HTTP Strict Transport Security (HSTS) is a proposed web security policy mechanism where a web server declares that complying user agents (such as a web browser) are to interact with it using secure connections only (such as HTTPS).

If a station security issue, you can use this firefox extension to force only https for all sites HTTPS Everywhere.

If a perimeter security issue, you can use a proxy forward server to redirect all http requests to https.

Finally, if you have a web server just make diferent paths for http and https. In https you will put your site and in http you will put just a index.html file using meta refesh. <meta http-equiv="refresh" content="0; url=https://example.com">